Estimate of the ionised chlorine abundance. The observed spectrum is shown as black dots. As indicated in the legend, three synthetic spectra are shown. The dotted grey curve has solar abundances across the board, and the dashed blue curve has nearly all abundances except for Cl adjusted to the values given in Table 3. The solid red curve is similar to the blue curve except that [Cl⁺ /H] has been increased by 3.14 dex.